Optical coherence tomography is an imaging technique that measures the interference between a reference beam of light and a detected beam of light that has impinged on a target tissue area and been reflected by scatterers within tissue back to a detector. In OCT imaging of blood vessels an imaging probe is inserted into a blood vessel and a 360 degree circular scan is taken of the vessel wall in series of segments of a predetermined arc to produce a single cross sectional image. The probe tip is rotated axially to create a circular scan of a tissue section and also longitudinally to scan a blood vessel segment length, thus providing two-dimensional mapped information of tissue structure. The axial position of the probe within the lumen remains constant with respect to the axial center of the lumen. However, the surface of the wall may vary in topography or geometry, resulting in the variance of the distance between the probe tip and the surface. Since conventional OCT imaging uses a fixed waveform to create the incident light beam in a schematically rectangular “window” of a certain height, the variation in surface height of the wall may result in the failure to gather tissue data in certain regions of the blood vessel wall. It would desirable to have a feedback mechanism that would cause the modification of the waveform to shift the window based on where the probe is and what it sees.
In traditional OCT systems, the length of the scanning line and its initial position have always been constant and fixed. One way to overcome this problem is to make the window larger. The problem with this is that the signal to noise ratio and accompanying sensitivity decrease because one is collecting information over a larger area in the same amount of time.
It would be desirable to use the identification of the tissue surface to adjust the starting position of the scan to a different spot. The identification of the surface could also be used to adjust the focal location in the sample arm. It would additionally be desirable if the identification of the attenuation of light within the tissue were used to adjust the scan range. The attenuation identification could also be used to determine an optimal depth of focus or confocal parameter.